The problem of air pollution generated by the use of automobiles and other motor vehicles is a major global environmental concern. Traditional gasoline burning internal combustion engines produce a great many products of incomplete combustion which are released into the atmosphere at the rate of millions of tons per year and which lead to a host of environmental problems, either themselves or as precursors of other pollutants formed by atmospheric chemical reactions. The search for cleaner alternatives has been extensive and is ongoing.
Motor vehicles which burn natural gas have recently been developed which produce significantly smaller amounts of pollutants. Major impediment to widespread use of such vehicles have been the problems of fuel availability and storage. The availability problem would seem to be easily solvable. Many residential and commercial buildings have a natural gas supply lines for heating and cooking, and tapping into these existing supply lines would seem to pose no great problem. However, the pressure in these supply lines is low, rendering the volume of the amount of natural gas required to power a vehicle over any practically useful distance too large to store and/or carry on board the vehicle.
Compressors are devices for converting a volume of compressible fluid at a given temperature and pressure to a smaller volume having a correspondingly higher pressure but preferably the same temperature. Such devices are useful for storage of gases, which are quite compressible and whose volumes vary inversely with pressure at constant temperature. Therefore a natural solution to the gas storage problem associated with natural gas powered vehicles is compression of the natural gas and storage of the compressed gas at a much higher pressure than is available from typical residential or commercial supply lines.
There are, however, problems associated with use of a compressor in this particular application. A typical compressor is substantially similar in its structure and operation to an internal combustion engine. Pistons for compressing the gas are reciprocated at high speeds within cylinders by piston rods connected to a crankshaft. Such a compressor comprises a large number of moving parts which are subject to large frictional forces, high temperatures, and therefore may wear and/or fail quickly. It has been estimated that a typical compressor used in this application would require a major overhaul and/or replacement on approximately a yearly basis, burdening a vehicle owner with considerable inconvenience and expense. In addition, such compressors are bulky, consume a large amount of power, are noisy, and generate large amounts of heat.
A hydraulically driven compressor is an alternative solution to this particular problem. The only power source required is a hydraulic power supply, which may be driven by an electric motor, runs quietly, and is durable, having fewer moving parts and requiring little maintenance. Higher final pressures may be attained with a hydraulically driven compressor. A hydraulically driven compressor may be driven slowly, significantly ameliorating problems associated with power consumption, friction, heat generation, and wear. In addition, the hydraulic power supply need only be connected to the compressor by supply and return lines for the hydraulic fluid, thereby allowing placement of the power supply far from the compressor itself. When dealing with high pressure combustible fluids such as natural gas, this may be a major safety advantage. Several examples of hydraulically driven compressors can be found in the patent literature, in particular U.S. Pat. Nos.: 4,390,322; 4,761,118; 5,238,372; and 5,464,330, each of which exhibit hydraulically driven pumps or compressors.
Gas liquefaction methods and/or apparatus are described in U.S. Pat. Nos.: 4,172,711; 4,456,459; 4,923,492; 5,473,900; 5,537,827; and 5,385,176.